The present invention relates to a device for protecting a flexural force receiver against overloading, particularly in weighing machines, in which a flexural force receiver is attached cantilevered at one end to a beam and the force to be measured is applied to the cantilevered end of the flexural force receiver.
The range within which flexural force receivers, particularly flexure bars, can be loaded beyond a prescribed maximum load without consequent damage, is relatively narrow. For customary commerical flexure bars it lies between 30 and 150% of the rated load. In weighing machines (balances or scales) an overload frequently occurs which may rise to 10 or more times the rated load, so that the need exists to protect the flexural force receiver from overloading or excessive bending.
Because of the short measurement stroke of the customary flexure bars, which is e.g., approximately 0.2 to 0.5 mm for a rated load of 10 kg, it is difficult to realise a rigid or stationary limit stop restricting the bending of the bar. Firstly the precise adjustment of such a stop presents problems and secondly with such short distances it is possible for faults to occur solely due to dirt.
In order to overcome these difficulties it is known to incorporate an auxiliary spring or other elastic intermediate element into the force introducing element of a flexure bar as overload protection means. When the flexure bar is loaded this elastic intermediate element expands by a considerably greater degree than the actual measurement stroke of the flexure bar, so that it is then possible to provide a fixed stop against which a specific part of the force introduction system strikes when the force introduced exceeds the rated load of the flexure bar.
However, these known constructions of overload protection devices for flexural force receivers have the following disadvantages: If the elastic intermediate element, e.g., a helicoidal spring, is made extremely soft, it is possible due to the comparatively great expansion range which can thereby be achieved to provide a precisely adjustable overload stop which allows sufficiently great play so that no faults can occur due to dirt, elastic deformations or other changes. However, the additional stroke dictated by a soft spring creates technical disadvantages for weighing, and in many cases cancels the peculiar advantage of virtually strokeless measurement by flexural force receivers. Moreover the incorporation of a soft auxiliary spring in a balance necessitates additional height, as a result of which one of the principal advantages of a flexure bar, namely the achievement of low height, becomes lost.
It is an object of the present invention to provide an overload protection device which permits a sufficiently great play towards a fixed stop but does not increase the height of the arrangement as is the case with the conventional interposition of a relatively soft elastic intermediate element.